Bleaching of wood



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v Patented Oct. 19, 1937 UNITED STATES n! e a PATENT OFFICE No Drawing.

Application August 29, 1935,

Serial No. 38,390

14 Claims.

My invention relates to the bleaching of wood and similar cellulosicmaterial and has particular reference to the bleaching of wood veneersand wood panels with hydrogen peroxide.

It has heretofore been proposed to effect the bleaching of wood withalkaline solutions of hydrogen peroxide but this has been attended withvarious disadvantages. Among the alkaline materials used have beencaustic soda, sodium silicates, and ammonia. Caustic soda has provenunsatisfactory because of its destructive action on the wood fibrewhereas the silicates possess the disadvantage of forming colloidaldeposits or films on the surface of the wood. All of the processes ofbleaching wood with alkaline solutions of hydrogen peroxide with which Iam familiar possess the important disadvantage that the bleaching actiontakes place essentially only upon the surface of the wood and does notpenetrate into the body proper thereof. Since, in staining wood veneersand the like, the veneers are preliminarily sanded whereby the surfacelayers of the wood are removed by abrasion, it is evident that, in orderto have a bleached surface remaining after the sanding of the veneers,the bleaching must affect not only the surface but also the interiorlayers of the wood. It is primarily because of this deficiency, namely,inability to bleach beyond the surface layers of the wood, thatbleaching with hydrogen peroxide has not come into more common use.

There are a number of woods which are of a relatively dark hue which areused to a considerable extent in the manufacture of furniture and. thelike and representative of which are certain varieties of mahogany andburl. These woods possess admirable properties for certain purposes buttheir more extensive use has been hampered by the fact that they possesstoo dark a color. It has been a desideratum to employ such woods formaking furniture, etc., but to impart thereto a finish of a lighter hue,for example, similar to walnut. Heretofore, to my knowledge, this hasnot been accomplished with complete success. The failure has been dueessentially to the fact that it has not heretofore been possible tosuccessfully bleach the wood so that the bleaching penetrates throughthe interior layers of the wood but such bleaching has affectedsubstantially only the surface. The subsequent necessary sanding withthe consequent removal of the under layers of the wood which have notbeen bleached makes it apparent that it is essential, if such dark woodsare to be given light finishes in furniture and the like, that thebleaching action exert itself to some fair extent below the surfaces ofthe wood.

I have discovered a method of bleaching wood and similar cellulosicmaterial, particularly in the form of veneers and panels, by means ofhydrogen peroxide and the like in which a markedly improved bleachingaction is obtained, particularly with regard to the penetration of thebleaching agent to a fairly substantial depth with the result that thebleaching action takes place not only on the surface of the wood or thelike but also extends somewhat into the interior. In general, Iaccomplish this result by subjecting the veneer or the like to apreliminary treatment with a solution of an organic base, after whichthe veneer is contacted with a solution of hydrogen peroxide or thelike. The nature of my invention will become clearer in the light of themore detailed description which follows.

It is accordingly an object of my invention to effect the bleaching ofwood and similar cellulosic material by means of hydroggrg pergxide andsimilar peroxides in a more effective manner than it has heretofore beenaccomplished.

Another object of my invention is the provision of an improved processfor bleaching wood veneers, wood panels, and the like.

A further object is to effect the bleaching of wood so that thebleaching action will take place to a substantial depth below thesurfaces of the wood, particularly with regard to those woods whichnormally possess a relatively dark hue or color.

Still another object is to effect the bleaching of Wood veneers, woodpanels, and the like by means of hydrogen peroxide and similar peroxideswhereby the bleaching action will be exerted to a substantial depthbelow the surface thereof.

A further object is to pr e l i rptnaljilylifgghdition wood or similarcellulosic material so that a bleaching agent will penetrate into thewood or similar cellulosic material to a substantial depth.

In carrying out my invention, in the case of the treatment of woodveneers, the veneer is preliminarily conditioned by being immersed in orotherwise contacted with a solution. of an organic base which does notform colored oxidation products. Among the organic bases which I havefound are suitable for my process are prill BUM lit! kylated derivativesof alkylolamines such as monoand di-methyl mono-ethanolamine, mono, di-,and tri-ethyl triethanolamine, and the like; alkyl amines such as butylamine, dimethyl amine, ethylene diamine, diethylene triamine,triethylene tetra-amine, and alkylated derivatives thereof such asmono-methyl ethylene diamine, 1,1-dimethyl ethylene diamine, mono ethyldiethylene triamine, and the like; aromatic and heterocyclic bases whichproduce a pH over '7 in aqueous media and which do not form coloredoxidation products such as benzyl amine, pyridine, and homologues andderivatives thereof and similar compounds.

After immersion in the organic base solution for the required length oftime, the conditioned veneer is removed, the excess of the organic basesolution is drained off, and the veneer is then immersed in a solutionof hydrogen peroxide preferably maintained at a temperature somewhatabove room temperature for a short period of time. It is then removedfrom the bleaching bath, washed with warm or hot water, and is thenready for drying and finishing.

As a specific example of carrying out my invention, I immerse a woodveneer in an aqueous solution of mono-ethanolamine containing about 10%of mono-ethanolamine by volume, which solution is previously brought upto a temperature of about 60 C. The veneer is maintained in this bathfor approximately fifteen to twenty minutes after which it is removedand drained to remove the excess of mono-ethanolamine adhering to thesurface of the veneer. The conditioned veneer is then immersed in a bathof 100 volume hydrogen peroxide (30% by weight of hydrogen peroxide),previously brought to a temperature of about 60 C., and allowed toremain in said bath for about fifteen to twenty minutes. Considerablecare should be taken when the conditioned veneer is immersed in thehydrogen peroxide solution since a semi-violent reaction takes placewhen the veneer contacts the hydrogen peroxide solution, oxygen beinggiven off and the hydrogen peroxide solution spattering about. Careshould be taken to prevent the hydrogen peroxide solution from touchingthe bare skin. In the event that some should contact the skin, asatisfactory antidote is cold water.

After immersion in the hydrogen peroxide solution for fifteen or twentyminutes, the veneer is removed and given a thorough washing with waterat a temperature of 60 C. to C. to wash out all traces of the hydrogenperoxide. The veneer is then dried and it may be finished in ways wellknown in the art. It will be found that the bleaching action has exerteditself to such an extent that the veneer is bleached for a distanceapproximately of an inch beneath the surface of the wood. It is evidentthat longer periods of immersion, more elevated temperatures, andgreater concentrations of materials will result in a greater depth ofthe bleaching action.

It is apparent that an assortment of veneers of different kinds can beimmersed in the same treating baths. In the illustrative embodimentdescribed hereinabove, measurements showed solution, it is necessaryonly to restore the amount lost so that the solution can be used overand over again.

In another example, I immersed a number of sheets of assorted woodveneers in an aqueous solution of ethylene diamine containingapproximately 10% of ethylene diamine by volume, the solution previouslyhaving been brought to a temperature of 60 C., and the veneers areallowed to remain in the solution for fifteen to twenty minutes. Theyare then removed and the excess liquor is allowed to drain off.

The thus conditioned veneers are then immersed in a bath comprisingvolume hydrogen peroxide, maintained at a temperature of about 60 C.,and allowed to remain therein for about fifteen to twenty minutes. Theyare then removed, rinsed well in warm water, dried and are then readyfor the finishing operations. As noted above, the reaction is quiteviolent when the conditioned veneers are immersed in the hydrogenperoxide bath and suitable precautions should be taken to preventcontact of the solution with the skin.

As has been stated above, and as is evident to those skilled in the art,certain modifications can be made of the processes which I havedescribed above by way of illustration only without departing from thespirit or true scope of the invention. For example, it is feasible toemploy weaker or stronger solutions of the organic base, say from 5% to15% solutions, in the preliminary treatment of the wood. The same istrue of the hydrogen peroxide solution. For example, I have obtainedgood results by using 75 volume hydrogen peroxide; that is, the 100volume solution may be diluted with 33% water, thereby effecting asaving in cost of materials. The temperature of the treating baths ispreferably from 50 C. to 70 C. The time of immersion in the treatingbaths and the temperature thereof may be cor related with theconcentration of the active ingredients in said baths in order to obtainthe desired bleaching effects, it being remembered that, withinoperative limits, higher concentrations, higher temperatures, andgreater period of treatment make for increased depth of bleachingaction. It is evident that other methods of contacting the organic baseand the hydrogen peroxide can be employed besides immersion. Forexample, the respective solutions may be brushed on or sprayed on theWood or the like. Immersion, however, produces highly satisfactoryresults.

Among the peroxide bleaching agents which are effective for my presentpurpose are organic per oxides such as urea peroxide, hydrogen peroxide,and the metallic peroxides such as sodium peroxide. With regard to thelatter, care must be taken that the solution of sodium peroxide in waterdoes not have such a high degree of alkalinity as to cause destructionor deterioration of the wood fibres. If sodium peroxide is used, it maybe advisable to neutralize the solution with an acid. Of all of theperoxides, I have found hydrogen peroxide to be the most suitable, andthe concentrations, temperatures and time of treatment described in theexamples hereinabove to give admirable results.

Among the woods which I have successfully treated by my process aremahoganies of different kinds such as African mahogany, Mexicanmahogany, mahogany crotch, walnut butt, walnut crotch, birds-eye maple,cherry burl and Va.- riovother types. The wood may be treated in thecreme; FLlllii CANON F TEXTILES & HBERS,

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form of panels or veneers or in any other desired shapes. It is obviousthat wood pulp, wood chips, and other cellulosic material such as papermay be similarly treated. It is further evident that the wood or thelike may be treated in a wet or dry state, that is, whether uncured orcured. It is also apparent that solvents other than water may be used inthe preliminary treatment step with the organic base. Among suchsolvents are those of an alcoholic nature such as ordinary ethylalcohol, light petroleum hydrocarbons, coal tar derivative solvents,benzol, acetone, chlorinated hydrocarbons such as carbon tetrachlorideand the like.

While I have described my invention in detail, it is clear that thedescription has been in terms of illustration and not limitation. Thescope of my invention is accordingly to be determined by the state ofthe art and the appended claims.

What I claim as new and desire to protect by Letters Patent of theUnited States is:

1. A process of bleaching wood and similar cellulosic materialcomprising preliminarily contacting said material with an organicnitrogenous base which does not form colored oxidation products, andthen contacting the material with an aqueous solution of a peroxide.

2. The process described in claim 1 wherein the organic base is analiphatic amine.

3. The process described in claim 1 wherein the organic base is analiphatic amine of the class consisting of mono-ethanolamine andethylene diamine.

4. The process described in claim 1 wherein the peroxide is hydrogenperoxide.

5. The process of bleaching wood, particularly in the form of veneersand panels, which comprises immersing the wood in an aqueous solution ofan aliphatic amine containing between 5% and 15% of the aliphatic amineat a temperature between 50 C. and 70 C. for from 15 to 30 minutes,removing the wood from the solution, immersing it in a solution ofhyrogen peroxide having a strength of approximately 75 to 100 volume andat a temperature of 50 C. to 70 0., maintaining the Wood therein forabout 15 to 30 minutes, removing the wood therefrom, and rinsing it withwarm water to remove the excess of hydrogen peroxide.

6. The process of bleaching wood veneers and the like comprisingimmersing the veneers in an aqueous solution of an aliphatic aminecontaining about of the amine, the solution being maintained at atemperature of approximately 60 C., maintaining the veneers in saidsolution for from about to minutes, removing the Veneers from saidsolution, removing the solution adhering to said veneers, immersing theveneers in 100 volume hydrogen peroxide main- 60 tained at a temperatureof approximately 60 C.

ma n door for approximately 15 to 20 minutes, removing the veneers,thoroughly washing them with hot water, and then drying them.

'7. The process described in claim 6 wherein the aliphatic amine is amember of the class consisting of mono-etha-nolamine and ethylenediamine.

8. The process of bleaching wood veneers and the like comprisingimmersing the veneers in approximately a 10% aqueous solution ofmonoethanolamine at a temperature of about 60 C. for betweenapproximately 15 and 20 minutes, removing the veneers from saidsolution, removing the excess adhering solution from the veneers,immersing the Veneers in '75 to 100 volume hydrogen peroxide maintainedat a temperature of about 60 C. for a period of from 15 to 30 minutes,removing the veneer, thoroughly washing it with warm water, and thendrying it.

9. The process described in claim 6 wherein the wood is of the classconsisting of mahogany, cherry burl, birds-eye maple and walnut.

10. The process of bleaching wood veneers or panels which comprisescontacting the Wood veneers or panels with an organic solvent solutionof an organic nitrogenous base which does not form colored oxidationproducts, removing the veneers or panels and contacting them with asolution of a peroxide, removing them from said latter solution,removing the excess of the peroxide, and drying the veneers or panels.

11. A light colored wood veneer or panel impregnated with an organicnitrogenous base and/or oxidation products thereof and resulting fromthe impregnation of a normally dark wood with an organic nitrogenousbase followed by a peroxide treatment.

12. A normally dark wood in the form of a veneer or panel, said woodbeing impregnated to a substantial depth below the surfaces thereof withan organic nitrogenous base and/or oxidation products thereof, and beingbleached to a relatively considerable depth beneath the surfaces thereofto render it light colored.

13. The product defined in claim 12, wherein the wood is bleached to atleast approximately of .an inch beneath the surfaces thereof.

14. The process of bleaching veneers or panels of Wood of the classconsisting of mahogany, cherry burl, birds-eye maple and walnut, whichcomprises contacting the wood veneers or panels with an aqueous solutionof an organic nitrogz enous base which does not form colored oxidationproducts, removing the veneers 0r panels and" contacting them with anaqueous solution of hydrogen peroxide, removing them from said lattersolution and rinsing with water to remove the excess of the peroxide.

WQLF KRITCHEVSK'Y.

